Engine-driven machines, such as dozers, loaders, excavators, motor graders, and other types of heavy equipment typically include a cooling system that cools the associated engine below a threshold temperature. The cooling system consists of one or more air-to-air or liquid-to-air heat exchangers that chill, among other things, coolant circulated throughout the engine and/or intake air directed into the engine. Heat from the coolant or intake air is transferred to air by a fan that is speed controlled based on temperatures of one or more of the various systems being cooled (e.g., engine).
Many cooling system fans are hydraulically powered. Specifically, a fan circuit may include a pump driven by the engine of the machine to draw in low-pressure fluid and discharge the fluid at elevated pressures to a motor that is connected to the fan. When temperatures are higher than desired, the fan circuit increases the speed of the fan. When temperatures are low, the fan circuit decreases the speed of the fan. However, due to a minimum inlet pressure requirement of the motor, the fan often has a limit on the minimum speed. Therefore, in some situations, for example, in cold ambient conditions, even when operating at the minimum speed, the fan may provide more cooling than is required or desired. This excessive cooling can cause icing of the engine inlet manifold.
One control strategy of preventing over cooling of the engine is described in U.S. Pat. No. 6,453,853 (the '853 patent) issued to Hawkins et al. on Sep. 24, 2002. Specifically, the '853 patent describes a strategy for controlling a hydraulic cooling fan. The control strategy reduces the possibility of engine overcooling during cold weather operation by turning the fan completely off whenever engine compartment temperatures are within acceptable limits and there is no request for fan speed.
Although the system of the '853 patent may reduce the likelihood of engine over cooling, it may still be less than optimal. Specifically, because the system of the '853 patent turns the fan completely off for an extended period of time, there is a risk that thermal shock of system components may occur when the fan is turned back on. Another control strategy to allow operation at lower temperatures is to raise engine speed and add loads to the system, but doing so greatly reduces fuel economy of the engine.
The cooling system of the present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems with existing technologies.